Fluorinated hydrocarbon compositions



Sept. 30, 1969 RD. BROADLEY 3,

FLUORINATEP HYDRQCARBON COMPOSITIONS Filed Oct. 3, 1963 CURVE A BOILING POINT (veo mm. H8 AT 0%.)

' Mon. MouoR LOROPE NTAFLUOROETHAN E T 'INVENTOYR ROBERT D. BROADLEY ATTORNEY United States Patent 3,470,101 FLUORINATED HYDROCARBON COMPOSITIONS Robert D. Broadley, Hanover Township, Morris County, N.J., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York Continuation-impart of abandoned application Ser. No. 179,237, Mar. 12, 1962. This application Oct. 3, 1963, Ser. No. 313,643

Int. Cl. C09k 3/06; F25

US. Cl. 252-67 -6 Claims This is a continuation-in-part of my application, Ser. No. 179,237, filed Mar. 12, 1962, now abandoned.

The invention relates to fluorinated hydrocarbons and more particularly to constant boiling fluorochlorocarbon mixtures which comprise difluoromethane and monochloropentafluoroethane and which are especially adapted for use as high capacity, low temperature refrigeration compositions.

The refrigeration capacity of a given amount of refrigerant is largely a function of boiling point, the lower boiling refrigerants generally offering the greater capacity at a given evaporator temperature. This factor to a great extent influences the design of refrigeration equipment and aflFects capacity, power requirements, size and cost of the unit. Another important factor directly related to boiling point of the refrigerant is minimum cooling temperature obtained in the evaporator during the refrigeration cycle, the lower boiling refrigerants being used to effect the lower refrigeration temperatures. For these reasons a large number of refrigerants of different boiling temperature and capacity are required to permit flexibility in design and the art is presented with the problem of providing new refrigerant-s as the need arises for new capacities and types of installations.

The lower aliphatic hydrocarbons when substituted by chlorine and fluorine are known to have potential as refrigerants. Many of these chlorofluorohydrocarbons exhibit certain desired properties including low cost, low specific volume, low toxicity and chemical inertness which have resulted in the extensive use of such compounds in a large number of refrigeration applications. Examples of such compounds include difluorodichlorornethane, B.P. 29.8 C., chlorodifluoromethane, B.P. 40.8 C., fluorodichloromethane, B.P. 8.9 C, fluorotrichloromethane, B.P. 23.8 C., and tetrafluorodichloroethane, B.P. 3.5 C. While these chlorine-fluorine derivatives provide an adequate range of refrigerants for many purposes, only a very few boil sufficiently low to offer any potential as low temperature refrigerants. A major reason for this is the presence of the heavier chlorine substituent which generally results in a higher boiling compound than those containing predominantly fluorine or hydrogen.

A compound having considerable potential as a low temperature refrigerant is difluoromethane, B.P. l.7 C. It has been found that this fluorocarbon posses many of the desired properties for use in refrigeration notwithstanding the presence of two hydrogen atoms which tend to induce flammability which is objectionable in some refrigeration applications. While fluorocarbons of this type are low boiling the limited number of such compounds having the desired refrigerant properties represent widely different boiling points and fail to provide a satisfactory range of low boiling refrigerants of different capacity. Increased activity in the field of eryogenics and low temperature e.g. quick freeze refrigeration gives rise to a need for new low temperature refrigerants representing different capacities than now available.

3,470,101 Patented Sept. 30, 1969 An object of the present invention is to provide new low temperatures, low cost compositions especially suitable for use as refrigerants. More particularly, it is an object to provide new refrigerants boiling lower and havmg greater capacity than the low boiling difluoromethane. Another object is to provide new low boiling compositions composed of difluoromethane mixtures which boil at substantially constant temperature and function as a substantially single substance and therefore are useful in producing refrigeration in those systems in which cooling is achieved by evaporation in the vicinity of the body to be cooled. A further object is to provide low boiling difluoromethane compositions which are substantially nonflammable.

In accordance with the invention it has been discovered that mixtures consisting of difluoromethane and monochloropentafiuoroethane containing approximately 30- 33 mol percent monochloropentafluoroethane form an azeotrope boiling at temperature of about 57 C. Unless otherwise indicated, percentages herein are in terms of mol percent. It has also been found that mixtures consisting of difluoromethane and monochloropentafluoroethane substantially in the range of 13-65% monochloropentafluoroethane have boiling points differing only slightly from the azeotropic composition. Compositions within this range will exhibit only negligible fractionation on boiling and represent useful refrigerants. Further, the mixtures formed by these components result in a reduction in the flammability of difluoromethane such that mixtures containing about 13% or more monochloropentafluoroethane are non-flammable in all proportions in the air.

The foregoing difluoromethane-monochloropentafluoroethane compositions with the minus 57 C. plus-minus 0.4 C. boiling temperature represent a marked reduction as compared with the boiling temperature of the lower boiling difluoromethane component. The indicated difluoromethane-monochloropentafluoroethane compositions may be employed to provide substantially increased refrigeration capacity over that of difluoromethane and represent new refrigerant compositions useful in obtaining high capacity low temperature refrigeration. Further, flammability of difluoromethane is reduced by admixture with monochloropentafiuoroethane such that all compositions within the indicated range are substantially nonflammable.

Boiling points of difiuoromethane-monochloropentafluoroethane mixtures were determined using diffuoromethane and monochloropentafluoroethane each better than 99.8 percent pure. All material was dried over P 0 prior to use. The static method was used to measure the boiling points of the mixtures. Weighed amounts of the components were distilled into a bomb and thermostated at constant temperature. To minimize the segregation error, the system was always 50-80% liquid filled. The vapor pressure was measured directly by a Wallace & Tiernan FA- mercury manometer which was accurate to better than 1 part in 1000, and all readings were corrected to normal atmospheric pressure of 760 mm. of Hg at 0 -C., and standard gravity. The bath temperature was controlled to better than :0.05 'C., and was measured by an L&N platinum resistance thermometer which was calibrated against an N.B.'S. certified platinum resistance thermometer. The accuracy of the temperature measurements was i0.02 C. Bath temperature was adjusted until the vapor pressure of the mixture was one atmosphere. The normal boiling point data are summarized as follows.

Normal boiling points of CH F /C F Cl mixture system M01 percent C F Cl Normal boiling An independent check was made on the azeotropic I composition by distillation. Approximately equimolar amounts of CH F and C F Cl were charged into a plate low temperature still. The still had provisions for sampling from the pot and the overhead. About /3 of the initial charge was distilled over at 57 C. This product was placed back in the still and refluxed until equilibrium was established. Samples were then taken from the overhead and the pot and analyzed by vapor phase chromatography. Analysis agreed within experimental error and by calibration of the chromatographs gave an azeotropic composition of 32%i1.0%'. The boiling point of this sample was determined in the above described static equipment, and was 57.26 C.

The data of the above table are represented graphically by the curve A of the attached drawing. The data and drawing show that the difluoromethane-monochloropentafluoroethane mixture system indicated forms a minimum boiling azeotrope within the approximately 30-33 mol percent range of C F Cl. As shown by the drawing, these data establish a curve having a relatively fiat lower contour demonstrating a range of mixture compositions having boiling points which vary only slightly from that of the minimum boiling minus 57.3 C. 30-33% C F Cl compositions. Curve A shows this range to consist of mixture compositions containing about 13-65% inclusive of C F Cl. The l3-65% chloropentafluoroethane compositions indicated each has a boiling temperature variation of less than 0.75 C., from the minimum boiling minus 57.3 C. azeotrope composition. As compositions containing 13-65% C F Cl all boil between about 56.6 C. and 57.3 C., representing a maximum boiling temperature variation within 0.75 C., no significant fractionation occurs on distillation of any compositions within this range, and all such compostions are suited for use as refrigerants.

For most advantageous refrigerant use, it is desirable and preferred to employ mixtures substantially at the 30-33% C F Cl azeotrope compositions if the objective is to avoid even minor differences in liquid and vapor composition. However, since there is no significant boiling point difference in the C F Cl composition range of -35%, for general first class operation these compositions are preferred. In cases where operating requirements are less rigid, compositions in the 15-55% C F Cl range, all boiling about at or below 57 C., are preferred and are eminently suitable since all such compositions boil within substantially 0.25 C.

Apart from use of the indicated amounts of difiuoromethane and monochloropentafluoroethane, make-up of the compositions of the invention requires no special procedures. The difiuoromethane and monochloropentafluoroethane employed should be substantially pure, preferably at least about 99.0 percent pure, and contain no substances deleteriously affecting the boiling characteristics of the mixture compositions or use as refrigerants.

The system formed by herein mixtures of difiuoromethane and monochloropentafiuoroethane provides a broad range of mixture compositions which boil at substantially constant temperature and give a constant boiling composition. These azeotropic and substantially azeotropic mixtures differ from refrigerant mixtures proposed in the past which offer only a relatively narrow range of useful compositions. While prior mixtures boil generally only about 1-3 C. below the lower boiling component, the mixture system of the present invention results in a relatively large reduction of about 5.0-5.5 C. over the boiling point of difiuoromethane. The compositions of the invention may be used in design of refrigeration equipment of reduced size operating at evaporator temperatures of about minus 15 and below to e.g. minus 70-80 C.

The compositions of the present invention exhibit the desired refrigerant properties including low cost, low specific volume, non-toxicity, and chemical inertness, with mixtures containing about 13.0% or more C F Cl being non-flammable in all proportions. In elfect, these compositions combine the valuable refrigerant characteristics of the chlorofluorohydrocarbons with the high capacity, low boiling properties of difiuoromethane. The substantially constant boiling properties of mixtures containing 13-65% of C F Cl provide a substantial range of compositions suitable for use in those types of refrigeration in which cooling is effected by condensing and thereafter evaporating the refrigerant in the vicinity of a body to be cooled. As refrigerants these compositions may be also used in the special situation known in the art to provide additional capacity where needed in equipment designed for difiuoromethane or refrigerants having equivalent capacity. It will be noted that the mixture system disclosed herein may also be used for other purposes including a heat transfer medium, gaseous dielectric, low temperature solvent and power fluid.

I claim:

1. A low boiling composition consisting of a mixture of difiuoromethane and monochloropentafluoroethanc, in which mixture the mol percent of monochloropentafluoroethane is substantially in the range of 13-65.

2. A low boiling composition consisting of a mixture of difiuoromethane and monochloropentafluoroethane, in which mixture the mol percent of monochloropentafluoroethane is substantially in the range of 15-55.

3. A low boiling composition consisting of a mixture of difiuoromethane and monochloropentafiuoroethane, in which mixture the mol percent of monochloropentafluoroethane is substantially in the range of 25-35.

4. The process of producing refrigeration which comprises condensing a mixture consisting of difiuoromethane and monochloropentafiuoroethane in which mixture the mol percent of monochloropentafiuoroethane is substantially in the range of 25-35, and thereafter evaporating said mixture in the vicinity of a body to be cooled.

5. The process of producing refrigeration which comprises condensing a mixture consisting of difiuoromethane and monochloropentafluoroethane in which mixture the mol percent of monochloropentafluoroethane is substantially in the range of 15-55, and thereafter evaporating said mixture in the vicinity of a body to be cooled.

6. The process of producing refrigeration which comprises condensing a mixture consisting of difiuoromethane and monochloropentafluoroethane in which mixture the mol percent of monochloropentafluoroethane is substantially in the range of 25-35, and thereafter evaporating said mixture in the vicinity of a body to be cooled.

References Cited UNITED STATES PATENTS 7/ 1934- Midgley et al 25267 6/1953 Iewis 25267 US. Cl. X.R. 62-1l2; 260-659 Po-mso Patent No. 3, 470,101

Inventor(s) m 185! UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated September 30 1069 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 59, "posses" should be -possesses--.

Claim 6, line 5, "25-35" should be -l365--.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer smuzu mu SEALED JAN 204970 WILLIAH E. SGHUYLER, JR. Comissioner of. Patents 

1. A LOW BOILING COMPOSITION CONSISTING OF A MIXTURE OF DIFLUOROMETHANE AND MONOCHLOROPENTAFLUOROETHANE, IN WHICH MIXTURE THE MOL PERCENT OF MONOCHLOROPENTAFLUOROETHANE IS SUBSTANTIALLY IN THE RANGE OF 13-65. 